The invention relates to the fracturing of subterranean formations, particularly in hydrocarbon well development or in hydrocarbon well renewal.
In the recovery of hydrocarbon values from subterranean formations, it is common practice, particularly in formations possessing low permeability, to fracture the hydrocarbon-bearing formation to provide flow channels to facilitate production of the hydrocarbons to the wellbore. In such fracturing operations, a fluid (fracturing fluid) is hydraulically injected down a well penetrating the subterranean formation and is forced against the formation by pressure. By this procedure, the formation is forced to crack or fracture, and proppant, generally solid particles designed to prop open the fracture when the fracturing pressure is released, is placed in the fracture. If the fracturing operation is successful, the crack or fracture developed provides improved flow of the recoverable fluid, e.g., oil or gas, into the well.
U.S. Pat. No. 5,439,055; U.S. Pat. No. 5,330,005; and U.S. Pat. No. 5,501,275 disclose procedures and compositions for treating subterranean formations to achieve improved recovery. The inventions of these patents are characterized by the use or presence of particulate materials and various solid materials, with emphasis on the formation of matrices of solid material and particulate material, or xe2x80x9cpacksxe2x80x9d, in the formation. Included among the wide variety of solid materials disclosed which may be employed in forming a pack or matrix are various types of fibrous materials, such as fibers of glass, ceramic, carbon, natural or synthetic polymers, or metal filaments. Important aspects of the procedures employed are the formation of stabilized matrices and prevention of proppant flowback from the subterranean formations.
While a wide variety of fluids may be used for fracturing, depending on the circumstances of the operation, a typical fracturing fluid, including the initial or xe2x80x9cpadxe2x80x9d fluid (no proppant) employed, preferably comprises or is composed of a thickened or gelled aqueous solution. Upon or after initiation of the fracture by the pad, the gelled or thickened fluid commonly utilized in the fracture extending step has suspended therein the proppant particles, the latter being substantially insoluble in the fluids of the formation. Suitable proppant materials include, but are not limited to, sand, walnut shells, sintered bauxite, or similar materials. A fuller description of fracturing procedure is found in U.S. Pat. No. 4,470,915 to Conway.
In order to achieve these steps, the fluid selected for fracturing commonly comprises a liquid whose viscosity is sufficient to transport proppant downwell in suspension, and which may be gelled or formulated to thicken or gel for assisting opening or extension of the fracture and deposit of the proppant in the fracture. In one known procedure, for example, the proppant carrying fluid, which contains a gelling agent or gellant and a crosslinking agent to crosslink the gellant, also contains a retarding agent which delays the crosslinking action of the crosslinking agent upon the gellant until the fracturing operation is imminent or is commenced. However, as is well understood by those skilled in the art, upon completion of the fracturing operation, to insure recovery of the desired hydrocarbons, it is necessary to remove or xe2x80x9cbreakxe2x80x9d the gel in the fracture created so that flow of the hydrocarbons through the fracture and proppant pack and into the wellbore is accomplished. To this end, a variety of xe2x80x9cbreakerxe2x80x9d compositions and xe2x80x9cbreakingxe2x80x9d procedures have been developed.
In particular, breakers which have been employed include various enzymes. (U.S. Pat. No. 5,067,566), and carboxylic acid esters (U.S. Pat. No. 5,223,159). U.S. Pat. No. 4,848,467 discloses the use of hydroxyacetic acid condensation product in a fracturing procedure which employs a hydrolyzable aqueous gel. According to the last mentioned patent, the hydroxyacetic acid condensation product, a low molecular weight polymeric material, functions as a fluid loss additive and further degrades at formation conditions to provide hydroxyacetic acid which breaks the aqueous gel, restoring formation permeability without the need for separate addition of a gel breaker. The commercial utility of this procedure is not known.
Notwithstanding the developed state of breaker procedures, room for improvement has existed. For example, while xe2x80x9cbreakerxe2x80x9d compositions are well known, such compositions, with the exception of the aforementioned composition of U.S. Pat. No. 4,848,467, generally perform little or no additional function in the fracture fluid suspension, and may be said to be simply along for the ride down the well. Accordingly, a novel breaker approach, which would provide additional benefits, at least in some embodiments, might have significant technical and commercial advantage. The invention provides such an approach.
Broadly, the invention relates to a novel and improved manner of breaking a fluid suspension gel. More particularly, the invention relates to an improved fracturing process or method, and novel fracturing composition or suspension, the invention being characterized by an improved breaker mechanism. In a particularly advantageous aspect, the invention provides a novel method of fracturing featuring improved matter transfer or mobility, e.g., improved downwell proppant and/or other solids transport, along with or combined with improved gel breaker means. In yet another embodiment, the invention provides a method of fracturing, including the provision and use of a fracturing fluid suspension containing an effective amount of a solid particulate breaker material having delayed breaking or degradation characteristics, additionally including an amount of durable fibers and/or platelets sufficient to enhance wellbore solids, such as proppant, transport.
Accordingly, in one aspect, solid particulate matter, which comprises or is composed of a specified organic polymeric compound or composition having an average molecular weight of at least 10,000, or a mixture of such compounds or compositions, and which solid organic polymeric matter reacts or decomposes, as described hereinafter, is provided in a fracturing fluid with or containing a specified gellant and proppant to form a fracturing fluid suspension, and the suspension formed is pumped downwell and deposited as a gelled suspension in the subterranean formation, generally under fracturing conditions. As used herein, the term xe2x80x9cparticulate matterxe2x80x9d refers to small discrete particles, portions or fragments, in all possible shapes, including fibrous materials (fibers) and/or platelets, of the specified organic polymeric material(s), as described more fully hereinafter. Commonly, the solid organic polymeric particulate matter is provided in the suspension in at least an amount sufficient (or sufficient amount) to provide over time an amount or concentration of a composition or compositions effective to degrade or decompose the gelled suspension in the formation either completely or to the desired degree. In the usual case, an amount of organic polymeric particulate matter, as described hereinafter, is utilized which provides an amount of its reaction, or degradation or decomposition products, upon reaction with or decomposition of the organic polymeric particulate matter over time in the downwell environment, as also defined hereinafter, effective to degrade or decompose the gelled suspension, more than one mechanism for breaking the gelled suspension being possible. Accordingly, by allowing the organic polymeric material to react or decompose in the downwell environment or downwell conditions, the amount of the organic polymeric particulate matter reacted or decomposed is thus effectively xe2x80x9cremovedxe2x80x9d from the fracture by its reaction or decomposition in the fracture, one or more ultimate products from such reaction or decomposition degrading or reacting with the gel or gelled suspension, or one or more of the gel""s components, and thereby decomposing or breaking the gel. Alternatively, other breaker compositions may be present, in desired amounts, so that the breaking procedure of the invention may be adapted to fine control by the operator.
While the breaker mechanism discovery of the invention is suited to any conventional fracturing procedure, the invention is particularly adapted to fracturing procedures employing fibers and/or platelets for strengthening the proppant pack, particularly if the organic polymeric particulate matter employed is also in the form of fibers. Additionally, regardless of the proppant pack characteristics in the fracture, the invention is particularly advantageous in the fracturing of high temperature subterranean formations, e.g., subterranean formations having a temperature of from about 225xc2x0 F. or higher. In particularly preferred embodiments, suitable adjustment of the breaker composition, including variation of or use of multiple particle sizes or organic polymeric material types, and/or pH control, allows improved and advantageous timing of the gel breaking operation.
In yet a further aspect, the invention comprises a novel fracturing fluid composition or suspension for carrying out the aforementioned procedures and features. Such compositions may also include components for pH adjustment for both gel formation and for aiding or retarding reaction or decomposition of the aforementioned organic polymeric particulate matter. Unless otherwise specified or evident from the context, all percentages given herein are by weight, based on the weight of the fluid. Other variations and aspects of the invention will be apparent from the further description herein and appended claims.